1. Field of the Invention
The present invention relates to network technology. More particularly, the present invention relates to methods and apparatus for encapsulating a frame for transmission in a storage area network.
2. Description of the Related Art
When interconnecting computers and other devices in a network, it has become desirable to create “virtual local area networks” (VLANs), in which all devices coupled to a VLAN receive all frames or packets which are universally addressed (whether by broadcast, multicast, or some other technique) on that VLAN, and in which all frames or packets which are universally addressed by a device on a VLAN are not distributed to devices outside the VLAN. The VLAN approach is particularly desirable when a single physical infrastructure is to be made available to multiple parties, each requiring that its data be kept private from the other parties. Further, the VLAN approach protects network entities on a given VLAN from failures of devices on the same infrastructure but belonging to a different VLAN.
Various VLAN transport protocol technologies have been proposed and come to be accepted in the art. For example, VLAN technologies which are now common include LANE (for ATM LAN-Emulation), IEEE Standard 802.10, and various proprietary schemes such as Inter-Switch Links (ISL) (e.g., for Cisco Catalyst.TM. Inter-Switch Links).
In order to allow multiple VLANs to share a single inter-switch link on the underlying physical topology, the interswitch link protocol (ISL) was developed at Cisco Systems. See for example U.S. Pat. No. 5,742,604, entitled “Interswitch link mechanism for connecting high-performance network switches,” Edsall, et al., issued on Apr. 21, 1998 to Cisco Systems, Inc., which is hereby incorporated by reference for all purposes. ISL provides an encapsulation mechanism for transporting packets between ports of different switches in a network on the basis of VLAN associations among those ports
Although ISL supports multiple VLANs on a single underlying network topology, certain limitations have been observed. Some of these limitations prevent easy implementation of ISL on modem storage area networks (SANs).
In recent years, the capacity of storage devices has not increased as fast as the demand for storage. Therefore a given server or other host must access multiple, physically distinct storage nodes (typically disks). In order to solve these storage limitations, the storage area network was developed. Generally, a storage area network is a high-speed special-purpose network that interconnects different data storage devices and associated data hosts on behalf of a larger network of users. However, although a SAN enables a storage device to be configured for use by various network devices and/or entities within a network, data storage needs are often dynamic rather than static.
A SAN may use various types of network traffic such as Ethernet or Fibre Channel frames. Regardless of the technology used, current SAN technology requires that a single protocol (e.g., Fibre Channel) be used throughout a particular SAN. Thus, current technology fails to address the need for supporting a multiple SAN system in which different transport protocols or technologies simultaneously co-exist. Note that ISL was originally designed for encapsulation of Ethernet packets. It does not support multiple different protocols on a single physical network infrastructure.
Ethernet is currently the most widely-installed LAN technology. The most commonly installed Ethernet systems are 10BASE-T systems, which provide transmission speeds up to 10Mbps. Alternatively, fast Ethernet systems, 100BASE-T systems, provide transmission speeds up to 100 megabits per second, while Gigabit Ethernet provides support at 1000 megabits per second (or 1 billion bits per second).
While Ethernet is widely used, use of fibre channel is proliferating in systems which demand high bandwidth and low latency. More specifically, the fibre channel family of standards (developed by the American National Standards Institute (ANSI)) defines a high speed communications interface for the transfer of large amounts of data between a variety of hardware systems such as personal computers, workstations, mainframes, supercomputers, storage devices and servers that have fibre channel interfaces. Fibre channel is particularly suited for connecting computer servers to shared storage devices and for interconnecting storage controllers and drives. Moreover, fibre channel is capable of transmitting data between computer devices at a data rate of up to 1 Gbps (or 1 billion bits per second), and a data rate of 10 Gbps has been proposed by the Fibre Channel Industry Association. Accordingly, fibre channel is a technology that is in widespread use for transmitting data in SANs. However, as indicated above, ISL was not optimized for fibre channel transmissions.
In view of the above, it would be desirable if properties of a VLAN could be merged with those of a SAN to enable various storage devices to be logically assigned to various entities within a network. Moreover, it would be beneficial if a single switching mechanism could simultaneously support different transport protocols (including at least fibre channel) within a network such as a SAN.